Dear Dr. Locker: My husband and I had sex on a Friday night, and two days later, I detected my LH surge using an ovulation predictor test stick. Is there a chance that I got pregnant even though we had sex before ovulation occurred? How long does sperm live inside a woman to fertilize an egg?
Answer from Dr. Locker
Sperm can live inside of a woman for one to four days. An egg is ready to be fertilized for one to (sometimes) two days. An ovulation predictor test stick detects the surge of LH that occurs between 24 hours and 36 hours *before* the egg is ready to be fertilized. Therefore, if you have sex on a Friday, surge on Sunday, you may have an egg ready to be fertilized on Sunday, Monday or perhaps Tuesday. The sperm that was deposited into you on Friday may possibly still be alive and able to fertilize your egg, but the chances are lower than if you had had sex on Sunday. The chance of becoming pregnant increases if you have sex when you are ovulating, or the day before. For more information about exactly how to chart your most fertile days, and how often and when to have sex, please read the directions that came in the box with the ovulation predictor test sticks that you bought. Also, please check out this book, which will give you much more detailed information about how to time sex in order to get pregnant: Taking Charge of Your Fertility: The Definitive Guide to Natural Birth Control, Pregnancy Achievement, and Reproductive Health by Toni Weschler.
For more info, you may also want to check out my answers to these questions:
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